The report shows that, during a quarter in which email volumes are at their highest, email opens on smartphones remained strong at 51%. Opens were highest early in the morning, and late at night, indicating that recipients check email on waking and before going to sleep.

However, the data also indicates that many return to their messages later in the day, or the next day, on desktop. High read lengths on desktop (15+ seconds) were second only to iPhone, at 52% and 55% respectively. Desktop opens remain steady throughout the day, but lower than than smartphones overall.

An interesting finding is that the UK is unique in that open rates on tablets are higher than the US - 25% versus 15%. Furthermore, read lengths on tablets are fairly high, more so on Android tablets where 48% of people spent 15+ seconds reading.

"Smartphones reign supreme, but tablets are also huge in the UK," concludes Movable Ink. "That's why it's incredibly important to optimize your emails for every device - desktop, mobile and tablet - and test on each of these, too."